Given the risk of increasing carbon emissions when using a pollution-generating energy source with limited reserves, such as fossil oil and natural gas, high-tech industries are pursuing replacement of the traditional energy sources with renewable and clean energy sources, including solar energy, hydraulic energy and wind energy. With this trend, vehicles with electric propulsion are being deployed in place of conventional internal combustion cars. The development of electric-powered vehicles has thus attracted great interest in the related fields.
An electric-powered vehicle requires a large quantity of power for long-distance running and, therefore, must be equipped with a good number of battery cells in its energy source. For a compact car with a 100-kilometer driving range, a 30 kWh battery pack is needed. It would require 3,000 of 18650 format battery cells arranged in parallel and in series in a battery pack to provide the required current and voltage levels to power the vehicle. Design a battery assembly that can meet safety, performance and operating life are critical to the success of an electrical vehicle. Prevention of vehicle fires due to battery thermal runaway is an important safety feature. It is unavoidable to have some cells exhibit thermal runaway due to manufacturing defects, assembly defects, or external impact event, but it is not acceptable for the small number of cells under thermal runaway to propagate into full pack fires.
A solution to the problem was proposed by some manufacturers, where the respective battery cells were coated by fire-proof material to prevent the battery cells from being ignited by adjacent cells under thermal runaway. During discharging or charging operations, a battery cell will generate heat, causing a temperature rise in the battery cells. Given the common battery configuration where positive and negative electrodes are at opposite ends, most heat dissipation is through the lateral side of the battery cell. In the case where the battery cell is covered at its lateral side with refractory material, the heat transfer is impeded and the battery cell ran hotter. Hotter battery cell lowers operating life. For every 10 degrees Celsius rise, the operating life is halved. Furthermore, battery cell with diminished heat dissipation capacity has an increased risk of thermal runaway, because battery self-heating could gradually build up to higher temperatures, causing electrolyte to decompose, surface electrolyte interface to degenerate, and various other chemical reactions to accelerate until the temperature rises to several hundred degrees Celsius and the cell ruptures and vents with very high temperature gas, over 1,000 degrees Celsius that could ignite adjacent materials.
A conventional method for fastening battery cells involves placing the battery cells into an accommodation space defined by a housing and then filling up the accommodation space with adhesive glue, whereby the battery cells are fastened within the accommodation space when the adhesive glue is cured. However, this method consumes a great amount of adhesive glue and increases the manufacture cost. Meanwhile, since the battery cells are generally covered by adhesive glue, the heat dissipation from the battery cells is largely reduced, thus causing a rise in operating temperature that leads to lower useable life. An adhesive stop mechanism allows a fixed amount of glue be placed on each cell, therefore the quality of bonding is assured with no waste in glues. Furthermore, by judicious design of the depth of said adhesive stop, the adhesive bonding area of the cell can be varied. For regions where the vibration is expected to be worse, more bonding area can be allocated, for regions where the vibration is expected to be less, for example with close proximity to fastening systems, the bonding area can be lessened.
In addition, the adhesive bonding area of the cell has lower thermal conductivity, and judicious design of the depth of said adhesive stop changes the heat dissipation capability of the battery cell. In an air cooled battery module, cells near the air inlet can be made to have worse heat dissipation, where the air is cooler. Cells near the air outlet can be made to have better heat dissipation, where the air is hotter. Since the life of the battery module is determined by the highest cell temperature, current invention effectively even out the temperature differences within the module, lowers the highest temperature of the cell group, with the desired effect of increasing battery module life.
In an electric vehicle battery assembly, no matter whether the battery cells provided therein are connected in parallel or in series, the positive and negative electrodes of the battery assembly are usually connected to the same side of the system through electric wires, so as to facilitate the installation and maintenance works. However, extra electrical wiring means extra burden to keep them organized in the compact space of the battery pack. The management of the complicated electric wires during the replacement, repair and maintenance of battery assemblies is a burdensome and safety hazardous task for installation and maintenance personnel.
Therefore, there is a need for a reliable adhesive-bonded battery assembly architecture, in which battery cells are mounted in a stable and robust manner to withstand vibration and have improved heat dissipation capability and prolonged endurance, and in which a highly effective thermal conductive device is mounted to lower the risk of cell thermal runaway, thereby safeguarding the safety of personnel and property. Advantageously, the battery assembly can be easily installed and maintained to save the manpower and time.